crc32

Description

Generates the cyclic redundancy checksum polynomial of 32-bit
lengths of the str. This is usually used
to validate the integrity of data being transmitted.

Warning

Because PHP's integer type is signed many crc32 checksums will
result in negative integers on 32bit platforms. On 64bit installations
all crc32() results will be positive integers though.

So you need to use the "%u" formatter of sprintf() or
printf() to get the string representation of the
unsigned crc32() checksum in decimal format.

For a hexadecimal representation of the checksum you can either use the
"%x" formatter of sprintf() or printf()
or the dechex() conversion functions, both of these
also take care of converting the crc32() result to
an unsigned integer.

Having 64bit installations also return negative integers for higher
result values was considered but would break the hexadecimal conversion
as negatives would get an extra 0xFFFFFFFF######## offset then. As
hexadecimal representation seems to be the most common use case we
decided to not break this even if it breaks direct decimal comparisons
in about 50% of the cases when moving from 32 to 64bits.

In retrospect having the function return an integer maybe wasn't the
best idea and returning a hex string representation right away (as
e.g. md5() does) might have been a better plan to
begin with.

For a more portable solution you may also consider the generic
hash(). hash("crc32b", $str) will
return the same string as str_pad(dechex(crc32($str)), 8, '0', STR_PAD_LEFT).

Parameters

str

The data.

Return Values

Returns the crc32 checksum of str as an integer.

Examples

Example #1 Displaying a crc32 checksum

This example shows how to print a converted checksum with the
printf() function: